1. Field of the Invention
The present invention relates to the fabric belts used on papermaking machines to support, carry and dewater a wet fibrous web as it is being processed into paper. More particularly, it relates to seamed, rather than endlessly woven, fabrics and to the joining of the two ends of a pin-seamable fabric to one another to form an endless belt on a papermachine.
2. Description of the Prior Art
Endless fabric belts are key components of all three sections (forming, pressing and drying) of the machines on which paper is manufactured. There, like a conveyor belt, they carry a wet fibrous web along as it is being processed into paper. At the same time, they provide needed support to the fragile wet paper web and dewater it by accepting water which drains or is pressed therefrom.
Generally, these fabrics are supplied either in endless form, that is, woven in the form of an endless loop without a seam, or in open-ended form. The later must be closed into endless form when installed on the papermachine. This will require a seam running in a substantially transverse direction across the fabric at the point where the two ends meet.
The so-called OMS (on-machine-seamed) fabrics are much easier to install on a papermachine position than those of the endlessly woven variety. To do so, one must draw one end of the open-ended fabric through the machine and around the relevant guide and tension rolls and other components. Then, the two ends may be joined to each other at a convenient location on the machine and the tension adjusted to make the fabric taut. In practice, a new fabric is often installed at the time a used one is being removed by connecting one end of the new fabric to the used fabric, which can then be used to pull the new fabric into proper position on the machine.
Alternatively, a rope, or ropes, may be attached to one end of a fabric being replaced. When the other end of the used fabric is pulled out to remove it from the machine, the rope, or ropes, is drawn about the path formerly occupied by the fabric. This approach enables plant personnel to clean machine components before the new fabric is installed. To complete the entire operation, one end of the rope is attached to the leader of the new fabric, while the other end is pulled to draw the fabric onto the machine position.
The closure of a commonly used variety of seams will be our primary concern here. The seams of interest are commonly referred to as pin seams. By deliberate design, it is more difficult to distinguish from the main body of the fabric than seams formed in other ways. The seam region in a fabric closed with a pin seam more closely resembles the main body of the fabric, in terms of such parameters as permeability, than the seam regions in fabrics seamed in other ways.
A pin seam can be quite difficult to close. To do so, a thin cable, known as a pintle, is directed through a tubular passage formed by the interdigitation of the seaming loops provided at the two ends of the fabric. The seaming loops in an OMS fabric are formed by the machine-direction, or longitudinal, body yarns of the fabric.
Typically, the pintle will be attached to a wire leader by means of a connecting sleeve. The leader, because of its stiffness relative to that of the pintle, will be directed through the tubular passage first, and used to pull the pintle therethrough as a needle may be used to pull a thread.
The pintle itself may be a monofilament extruded from any of the synthetic polymeric resin materials used in the manufacture of the papermachine clothing. Such a pintle may have either a round (circular) or flattened (elliptical) cross section. Alternatively, the pintle may take any one of the other forms commonly taken by the yarns used in the weaving of papermachine clothing; that is to say, pintles may take the forms of braided or plied monofilament yarns, multifilament yarns or spun yarns, and so forth.
Even after a pintle has been installed, it remains necessary to ensure that the seam region has the same properties, in terms of permeability and compressibility, as the main body of the fabric, so that the seam region will not "mark" the paper sheet being manufactured. At the very least, marking of this sort is aesthetically undesirable; at worst, the mark represents a weakness in the sheet susceptible to breakage. In addition, where the permeability of the seam region is different from that of the main body of the fabric, an extremely loud "popping" noise may be generated each time the seam region passes over a suction box. One of ordinary skill in the art would readily acknowledge such persistent and repetitious "popping" to be an annoyance.
Stuffer yarns are frequently used to provide the seam region with permeability and compressibility comparable to those of the main body of the fabric. In the past, stuffer yarns have been installed separately following the installation of the pintle to fill in any void volume remaining around the pintle in the passage formed by the interdigitated seaming loops. Typically, the stuffer yarns have their own leader, but this must be fed or directed through the passage already occupied by the pintle itself. Quite often, the seaming loops themselves are damaged in the course of this separate operation.
The present invention is designed to permit the simultaneous installation of both pintle and stuffer yarn to reduce and optimally to eliminate the occurrence of seaming loop damage during the seaming operation.